Hello,
I sail an A-Cat and I have installed a Guck snuffer and I am very satisfied with this system. As the A-Cat is very light and the Guck snufferbag, although half the size of the Nacra snuffer, is a little baggy you will lose some upwind capability due to windage. BUT you will win a lot on the downwind leg. Enough so you can keep up with the Inter 20 and the Tornado.
On an A-Cat there is limited use for a spinaker as the spi will lift the boat out of the water with a lot of wind. I will use the spi till about 3 Bft. It is very good to check if you have any heartproblems. I believe that 3 Bft. is about 10 knts. Correct me when I am wrong.
I have a 15 m2 spi, so not a very large spinaker. On my Taipan 4.9 I had an EO snuffer and the much longer snufferbag pushed me away much more than the shorter Guck system.
Regards.
Arjan de Bruin
A-Cat 074